WO2010082272A1 - Semiconductor device and method for producing the same - Google Patents

Abstract

A semiconductor device which can satisfy both a reverse blocking property and a low on-resistance is provided.  The semiconductor device is comprised of a first semiconductor layer containing a channel layer; a source electrode formed on the first semiconductor layer; a drain electrode spaced from the source electrode on the first semiconductor layer; and a gate electrode formed between the source electrode and the drain electrode on the first semiconductor layer.  The drain electrode contains a first drain area in which a reverse current between the drain electrode and the first semiconductor layer is blocked, and a second drain area formed at a distance further away from the gate electrode than the first drain area, in which a resistance between the drain electrode and the first semiconductor layer is lower than the first drain area.

Description

Semiconductor device and manufacturing method thereof

The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly, to a semiconductor device having reverse blocking characteristics and a manufacturing method thereof.

As a highly efficient AC / AC power conversion method, a direct conversion type power conversion circuit represented by a matrix converter has attracted attention. In this circuit, power conversion is realized by a combination of bidirectional switches. Usually, a semiconductor switching device cannot maintain an off characteristic when a negative drain voltage is applied. Therefore, as shown in FIG. 9, a bidirectional switch has been realized by combining two series connection circuits of diodes and transistors.

The ON characteristics of such a bidirectional switch are schematically shown in FIG. 14A. Since this bidirectional switch is composed of a Schottky diode and an IGBT (Insulated Gate Bipolar Transistor), an on-voltage of 3 V is generated by adding 1 V of the diode and 2 V of the IGBT. As a result, the power in the hatched portion in the figure is lost as a loss by the switch.

If the switch part can be composed of a field effect transistor (FET), such a loss can be minimized. However, the FET usually does not have a so-called reverse blocking characteristic that prevents reverse current.

FIG. 10 schematically shows drain I (current) -V (voltage) characteristics of an FET that does not have reverse blocking characteristics. Even when the drain voltage is positive, the gate potential shifts to the positive side when the drain voltage becomes negative even under the gate voltage condition where the drain voltage is positive. As a result, the channel opens and reverse current flows. When a positive gate voltage V _G is applied, the reverse current increases as V _G1 , V _G2 , V _G3 and the gate voltage V _G increase.

On the other hand, FIG. 11 schematically shows the drain IV characteristics of an FET having reverse blocking characteristics. Even if the drain voltage is negative, the reverse blocking characteristic can be maintained regardless of the gate voltage V _G (V _G1 <V _G2 <V _G3 ). If such an FET is used, the bidirectional switch can be configured as shown in FIG. As a result, it is possible to reduce the cost by reducing the number of parts and downsizing by reducing the mounting area. Furthermore, the loss at the time of ON can be reduced by omitting the diode.

As a structure having reverse blocking characteristics as shown in FIG. 11, Patent Documents 1 and 2 propose FETs having a drain electrode as a Schottky contact. FIG. 13 shows the semiconductor device disclosed in FIG. A channel layer 101 made of an n-type SiC layer is formed on a semi-insulating substrate 105. On top of that, a source electrode 103 in ohmic contact and a drain electrode 102 in Schottky contact are formed. In addition, a gate electrode 104 is formed in Schottky contact between both electrodes. A metal layer 106 is formed on the back surface of the semi-insulating substrate 105. In the FETs disclosed in Patent Documents 1 and 2, when a negative voltage is applied to the drain electrode, the reverse bias is applied to the Schottky diode, and the drain current is shielded to achieve reverse blocking characteristics. Is done.

JP 2003-7976 A JP-A-1-202870

However, when a positive voltage is applied to the drain electrode, the on-resistance increases because the on-voltage of the Schottky diode is added to the on-characteristic of the transistor. The ON characteristics of the switch in this case are shown in FIG. 14B. Since the transistor is changed from IGBT to FET, the on-voltage is lowered, but the on-voltage of the drain Schottky portion remains about 1V. For this reason, when a bidirectional switch is constituted by transistors having such a configuration, there is a problem that the loss of the switch portion cannot be sufficiently reduced.

The present invention has been made in view of the above, and an object thereof is to provide a semiconductor device capable of achieving both reverse blocking characteristics and low on-resistance.

A semiconductor device according to the present invention includes:
A first semiconductor layer including a channel layer;
A source electrode formed on the first semiconductor layer;
A drain electrode formed on the first semiconductor layer and spaced apart from the source electrode;
A gate electrode formed between the source electrode and the drain electrode on the first semiconductor layer;
The drain electrode is
A first drain region in which a reverse current between the first semiconductor layer and the first semiconductor layer is blocked;
And a second drain region that is formed farther from the gate electrode than the first drain region and has a lower resistance to the first semiconductor layer than the first drain region.

A method for manufacturing a semiconductor device according to the present invention includes:
Forming a first semiconductor layer including a channel layer;
Forming a source electrode, a drain electrode, and a gate electrode between the source electrode and the drain electrode on the first semiconductor layer, and
The drain electrode is
A first drain region in which a reverse current between the first semiconductor layer and the first semiconductor layer is blocked;
And a second drain region that is formed farther from the gate electrode than the first drain region and has a lower resistance to the first semiconductor layer than the first drain region.

According to the present invention, it is possible to provide a semiconductor device that can achieve both reverse blocking characteristics and low on-resistance.

1 is a cross-sectional view illustrating a structure of a field effect transistor according to a first embodiment. 1 is a cross-sectional view illustrating a structure of a field effect transistor according to Example 1. FIG. It is a conceptual diagram which shows the ON characteristic and loss of the bidirectional | two-way switch using the field effect transistor which concerns on Embodiment 1. FIG. FIG. 6 is a cross-sectional view showing a structure of a field effect transistor according to a second embodiment. 6 is a cross-sectional view showing a structure of a field effect transistor according to Example 2. FIG. FIG. 6 is a cross-sectional view showing the structure of a field effect transistor according to a third embodiment. 6 is a cross-sectional view illustrating a structure of a field effect transistor according to Example 3. FIG. FIG. 6 is a cross-sectional view showing the structure of a field effect transistor according to a fourth embodiment. 6 is a cross-sectional view illustrating a structure of a field effect transistor according to Example 4. FIG. FIG. 10 is a cross-sectional view showing the structure of a field effect transistor according to a fifth embodiment. 10 is a cross-sectional view illustrating a structure of a field effect transistor according to Example 5. FIG. FIG. 10 is a cross-sectional view showing the structure of a field effect transistor according to a sixth embodiment. 10 is a cross-sectional view illustrating a structure of a field effect transistor according to Example 6. FIG. FIG. 10 is a cross-sectional view showing the structure of a field effect transistor according to a seventh embodiment. 10 is a cross-sectional view illustrating a structure of a field effect transistor according to Example 7. FIG. It is a figure which shows the circuit structure of a general bidirectional switch. It is a figure which shows the drain IV characteristic of the field effect transistor which is not provided with a reverse blocking characteristic. It is a figure which shows the drain IV characteristic of a field effect transistor provided with a reverse blocking characteristic. It is a figure which shows the circuit structure of the bidirectional | two-way switch using the transistor provided with a reverse blocking characteristic. FIG. 2 is a cross-sectional view of the field effect transistor disclosed in FIG. It is a conceptual diagram which shows the ON characteristic and loss of a general bidirectional switch. It is a conceptual diagram which shows the ON characteristic and loss of a bidirectional | two-way switch using the field effect transistor disclosed by patent document 1. FIG.

Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiment. In addition, for clarity of explanation, the following description and drawings are simplified as appropriate.

(Embodiment 1)
FIG. 1A is a cross-sectional view of a field effect transistor (FET) according to the first embodiment of the present invention. In this FET, an n-type channel layer 11 is formed on a substrate 10 made of, for example, GaAs. Further, on the channel layer (first semiconductor layer) 11, the source electrode 1 in ohmic contact, the first drain electrode (first drain region) 3 and the second drain electrode provided apart from the source electrode 1 are provided. A (second drain region) 4 is formed. Further, a gate electrode 2 that is in Schottky contact is formed between the source electrode 1 and the first drain electrode 3.

Here, the first drain electrode 3 and the second drain electrode 4 are at the same potential. The first drain electrode 3 disposed on the side close to the source electrode 1 forms a Schottky contact with the channel layer 11. On the other hand, the second drain electrode 4 disposed on the side far from the source electrode 1 forms ohmic contact with the channel layer 11. FIG. 1A shows a configuration in which the first drain electrode 3 and the second drain electrode 4 are separated and connected to the same potential by wiring or the like, but the first drain electrode 3 and the second drain electrode 4 are in contact with each other. You may do it.

In the FET according to the present embodiment, when a negative voltage is applied to the drain electrodes 3 and 4, the channel is pinched off in the region of the first drain electrode 3, the current flow is shielded, and reverse blocking characteristics are realized. On the other hand, when a positive voltage is applied to the drain electrodes 3 and 4, the region of the second drain electrode 4 having a low resistance becomes a current path, and a low on-resistance is obtained.

As the substrate 10, in addition to a semiconductor material such as GaAs, InP, SiC, Si, SiGe, or GaN, an insulator such as sapphire can be used as long as the channel layer 11 can be formed in the upper layer.

Further, as the channel layer 11, a group III-V compound semiconductor such as InGaAs, InGaP, or InAlGaN, or a group IV semiconductor material such as SiC, Si, or SiGe can be used. Further, the present invention is not limited to a single semiconductor layer, and a structure in which a plurality of layer structures having different impurity concentrations or an electronic layer formed at the interface by forming a heterojunction may be used as a carrier.

Although an example of Schottky contact is shown as the gate electrode 2, if a function for controlling current can be realized, a MIS (Metal-Insulator Semiconductor) structure in which a metal is arranged on a semiconductor through an insulating film, or a pn junction is provided. It is good also as the structure utilized. In FIG. 1A, all of the source electrode 1, the gate electrode 2, and the drain electrodes 3 and 4 are arranged on the same plane of the channel layer 11. For example, the gate is formed on the recess from which a part of the channel layer 11 is removed. The electrode 2 may be formed.

In the FET according to the present embodiment, when a negative voltage is applied to the drain electrodes 3 and 4, the channel is pinched off in the region below the first drain electrode 3, and the current flow is blocked. Thereby, the reverse blocking characteristic as shown in FIG. 9 is realized. On the other hand, when a positive voltage is applied to the drain electrodes 3 and 4, the region under the low-resistance second drain electrode 4 becomes a current path, and a low on-resistance is obtained. FIG. 2 is a conceptual diagram schematically showing the on characteristics of the switch constituted by the FET according to the present embodiment. As shown in FIG. 2, the drain current rises linearly from approximately 0 V, and the loss of the switch portion can be minimized. This enables a low-loss and low-cost bidirectional switch.

(Example 1)
Next, Example 1 which is a specific example of the first embodiment will be described. FIG. 1B is a cross-sectional view of the FET according to this example.

This FET is formed on a substrate 12 made of silicon or the like. On the substrate 12, a buffer layer 13 for relaxing lattice mismatch, a channel layer 14 made of In _x Ga _1-x N (0 ≦ x ≦ 1), and Al _y Ga _1-y N (0 <y ≦). An electron supply layer 15 comprising 1) is formed in order. In this embodiment, the buffer layer 13, the channel layer 14, and the electron supply layer 15 correspond to the first semiconductor layer. The range of 0 ≦ x ≦ 0.2 as the composition of the channel layer 14 and the range of 0.1 ≦ y ≦ 0.3 as the composition of the electron supply layer 15 is most suitable for a switching device for power control.

The source electrode 1 and the second drain electrode 4 are both formed on the electron supply layer 15 by ohmic contact. A first drain electrode 3 is formed by Schottky contact between the source electrode 1 and the second drain electrode 4 in a region close to the second drain electrode 4. Further, the same potential is applied to the first drain electrode 3 and the second drain electrode 4.

The surface of the electron supply layer 15 is covered with a surface protective film 21. In addition, in the opening (recess) formed between the source electrode 1 and the first drain electrode 3, the electron supply layer 15 and the gate electrode 2 constituting the MIS structure are formed via the gate insulating film 22. . A part of the gate electrode 2 plays a role of mitigating electric field concentration as a bowl-shaped field plate 20 mounted on the surface protective film 21.

Next, a method for manufacturing the FET according to Example 1 will be described. Here, GaN with a composition of the channel layer 14 x = 0 and Al _0.2 Ga _0.8 N with a composition of the electron supply layer 15 y = 0.2 are shown as an example. First, a buffer layer 13 (film thickness 20 nm) made of undoped AlN and a channel layer 14 (film thickness 2 μm) made of undoped GaN on a silicon substrate 12 by, for example, a molecular beam epitaxy (MBE) growth method. Then, an electron supply layer 15 (thickness 25 nm) made of undoped Al _0.2 Ga _0.8 N is formed in order.

Next, an element isolation mesa (not shown) is formed by etching away a part of the formed laminated structure until the channel layer 14 is exposed. Subsequently, a source electrode 1 and a second drain electrode 4 are formed on the electron supply layer 15 by evaporating a metal such as Ti / Al. And it is set as ohmic contact by annealing at 650 degreeC. Further, a metal such as Ni / Au is deposited on the electron supply layer 15 to form the first drain electrode 3 having a Schottky contact.

Subsequently, a surface protective film 21 made of SiN having a thickness of 50 nm is formed by a plasma CVD method or the like. The electron supply layer 15 is exposed by removing a part of the surface protective film 21 by etching. Further, the recess is formed by etching so that the threshold value becomes positive. A gate insulating film 22 made of SiO ₂ having a thickness of 150 nm is formed by, for example, atmospheric pressure CVD so as to cover the exposed electron supply layer 15. A metal film such as Ni / Au is vapor-deposited thereon to form the MIS structure gate electrode 2 having the field plate 20. Thus, the FET shown in FIG. 1B is manufactured.

The FET according to Example 1 has normally-off characteristics and can achieve a high breakdown voltage due to the electric field relaxation effect of the field plate. Therefore, it is suitable for a switching device for power control. In addition, when a negative voltage is applied to the drain electrodes 3 and 4, the channel immediately below the first drain electrode 3 is in a pinch-off state, so that the drain current is cut off and exhibits reverse blocking characteristics. On the other hand, when a positive voltage is applied to the drain electrodes 3 and 4, a drain current flows through the low-resistance second drain electrode 4, so that a low-resistance on-characteristic can be realized.

(Embodiment 2)
Next, a second embodiment of the present invention will be described with reference to FIG. 3A.
FIG. 3A is a cross-sectional view of the FET according to the present embodiment. The present embodiment is different from the first embodiment in that the first drain electrode 3 disposed at a position close to the source electrode 1 forms a MIS structure with the channel layer 11 via the insulating film 5. Since the other configuration is the same as that of the first embodiment, the description thereof is omitted.

In the FET according to the present embodiment, when a negative voltage is applied to the drain electrodes 3 and 4 as in the first embodiment, the channel is pinched off in the region under the first drain electrode 3 and the current flow is shielded. The reverse blocking characteristic is realized. On the other hand, when a positive voltage is applied to the drain electrodes 3 and 4, a region under the low-resistance second drain electrode 4 becomes a current path, and a low on-resistance is obtained. In addition, since the first drain electrode 3 has the MIS structure, the leakage current during the reverse blocking operation can be suppressed to be lower than that in the first embodiment.

(Example 2)
Next, Example 2 which is a specific example of the second embodiment will be described. FIG. 3B is a cross-sectional view of the FET according to this example.

This FET is formed on a substrate 12 made of silicon or the like. On the substrate 12, a buffer layer 13 for relaxing lattice mismatch, a channel layer 14 made of In _x Ga _1-x N (0 ≦ x ≦ 1), and Al _y Ga _1-y N (0 <y ≦). An electron supply layer 15 comprising 1) is formed in order. In this embodiment, the buffer layer 13, the channel layer 14, and the electron supply layer 15 correspond to the first semiconductor layer. The range of 0 ≦ x ≦ 0.2 as the composition of the channel layer 14 and the range of 0.1 ≦ y ≦ 0.3 as the composition of the electron supply layer 15 is most suitable for a switching device for power control.

The source electrode 1 and the second drain electrode 4 are formed on the electron supply layer 15 by ohmic contact. Further, the surface of the electron supply layer 15 is covered with a surface protective film 21. Two openings are formed between the source electrode 1 and the first drain electrode 4, and the gate electrode 2 and the first drain constituting the MIS structure with the electron supply layer 15 via the gate insulating film 22 respectively. An electrode 3 is formed. The first drain electrode 3 is disposed adjacent to the second drain electrode 4, and the first drain electrode 3 and the second drain electrode 4 are connected to the same potential. A part of the gate electrode 2 rides on the surface protective film 21 and serves as a field plate 20 having an eaves-like shape, and plays a role of reducing electric field concentration.

Next, a method for manufacturing the FET according to Example 2 will be described. Here, as an example, the composition of the channel layer 14 is GaN with x = 0 and the composition of the electron supply layer 15 is Al _0.2 Ga _0.8 N with y = 0.2. First, a buffer layer 13 (film thickness 20 nm) made of undoped AlN, a channel layer 14 (film thickness 2 μm) made of undoped GaN, and an undoped Al _0.2 Ga film on a substrate 12 made of silicon, for example, by molecular beam epitaxy. _An electron supply layer 15 (thickness 25 nm) made of _0.8 N is formed in order.

Next, an element isolation mesa (not shown) is formed by etching away a part of the formed laminated structure until the channel layer 14 is exposed. Subsequently, a source electrode 1 and a second drain electrode 4 are formed on the electron supply layer 15 by evaporating a metal such as Ti / Al. And it is set as ohmic contact by annealing at 650 degreeC.

Subsequently, a surface protective film 21 made of SiN having a thickness of 50 nm is formed by a plasma CVD method or the like. By removing a part of the surface protective film 21 by etching, two openings where the electron supply layer 15 is exposed are formed. Further, a recess is formed in the exposed electron supply layer 15 by etching so that the threshold value becomes positive immediately below the gate electrode 2. A gate insulating film 22 made of SiO ₂ having a thickness of 150 nm is formed by, for example, atmospheric pressure CVD so as to cover the exposed electron supply layer 15. A metal such as Ni / Au is vapor-deposited thereon to form the MIS structure gate electrode 2 and the first drain electrode 3 having the field plate 20. Thus, the FET shown in FIG. 3B is manufactured.

The FET according to Example 2 has normally-off characteristics and can achieve a high breakdown voltage due to the electric field relaxation effect of the field plate. Therefore, it is suitable for a switching device for power control. When a negative voltage is applied to the drain electrodes 3 and 4, the channel immediately below the first drain electrode 3 is in a pinch-off state, so that the drain current is cut off and exhibits reverse blocking characteristics. On the other hand, when a positive voltage is applied to the drain electrodes 3 and 4, a drain current flows through the low-resistance second drain electrode 4, so that a low-resistance on-characteristic can be realized. In addition, since the first drain electrode 3 has the MIS structure, the leakage current during the reverse blocking operation can be suppressed to be lower than that in the first embodiment.

(Embodiment 3)
Next, a third embodiment of the present invention will be described with reference to FIG. 4A.
FIG. 4A is a cross-sectional view of the FET according to the present embodiment. In the present embodiment, the first drain electrode 3 disposed at a position close to the source electrode 1 is interposed via a channel layer (first semiconductor layer) 11 and a p-type layer (second semiconductor layer) 16 having a different conductivity type. The difference from the first embodiment is that the channel layer 11 is formed. Since the other configuration is the same as that of the first embodiment, the description thereof is omitted.

In the FET according to the present embodiment, when a negative voltage is applied to the drain electrodes 3 and 4 as in the first embodiment, the channel is pinched off in the region under the first drain electrode 3 and the current flow is shielded. The reverse blocking characteristic is realized. On the other hand, when a positive voltage is applied to the drain electrodes 3 and 4, a region under the low-resistance second drain electrode 4 becomes a current path, and a low on-resistance is obtained.

Example 3
Next, Example 3 which is a specific example of the third embodiment will be described. FIG. 4B is a cross-sectional view of the FET according to this example.

This FET is formed on a substrate 12 made of silicon or the like. On the substrate 12, a buffer layer 13 for relaxing lattice mismatch, a channel layer 14 made of In _x Ga _1-x N (0 ≦ x ≦ 1), and Al _y Ga _1-y N (0 <y ≦). An electron supply layer 15 comprising 1) is formed in order. In this embodiment, the buffer layer 13, the channel layer 14, and the electron supply layer 15 correspond to the first semiconductor layer. The range of 0 ≦ x ≦ 0.2 as the composition of the channel layer 14 and the range of 0.1 ≦ y ≦ 0.3 as the composition of the electron supply layer 15 are most suitable for the switching device for power control. A p-type layer 16 made of GaN is formed on the uppermost layer.

The source electrode 1 and the second drain electrode 4 are both formed on the electron supply layer 15 by ohmic contact. The first drain electrode 3 is formed on the electron supply layer 15 between the source electrode 1 and the second drain electrode 4 and in the vicinity of the second drain electrode 4 via the p-type layer 16 made of GaN. . Here, the first drain electrode 3 and the second drain electrode 4 are connected to the same potential.

The surface of the electron supply layer 15 is covered with a surface protective film 21. In addition, in the opening formed between the source electrode 1 and the first drain electrode 3, the electron supply layer 15 and the gate electrode 2 constituting the MIS structure are formed via the gate insulating film 22. A part of the gate electrode 2 plays a role of mitigating electric field concentration as a bowl-shaped field plate 20 mounted on the surface protective film 21.

Next, a method for manufacturing the FET according to Example 3 will be described. Here, as an example, the composition of the channel layer 14 is GaN with x = 0 and the composition of the electron supply layer 15 is Al _0.2 Ga _0.8 N with y = 0.2. First, a buffer layer 13 (film thickness 20 nm) made of undoped AlN, a channel layer 14 (film thickness 2 μm) made of undoped GaN, and an undoped Al _0.2 Ga film on a substrate 12 made of silicon, for example, by molecular beam epitaxy. _An electron supply layer 15 (film thickness 25 nm) made of _0.8 N and a p-type layer 16 (film thickness 10 nm) made of GaN are formed in this order.

Next, an element isolation mesa (not shown) is formed by etching away a part of the formed laminated structure until the channel layer 14 is exposed. Subsequently, the p-type layer 16 is removed by etching except for the region where the first drain electrode 3 is formed, and the electron supply layer 15 is exposed. The source electrode 1 and the second drain electrode 4 are formed on the exposed electron supply layer 15 by evaporating a metal such as Ti / Al. And it is set as ohmic contact by annealing at 650 degreeC. Further, a metal such as Ni / Au is deposited on the electron supply layer 15 to form the first drain electrode 3.

Subsequently, a surface protective film 21 made of SiN having a thickness of 50 nm is formed by a plasma CVD method or the like. The electron supply layer 15 is exposed by removing a part of the surface protective film 21 by etching. Further, the recess is formed by etching so that the threshold value becomes positive. A gate insulating film 22 made of SiO ₂ having a thickness of 150 nm is formed by, for example, atmospheric pressure CVD so as to cover the exposed electron supply layer 15. A metal film such as Ni / Au is vapor-deposited thereon to form the MIS structure gate electrode 2 having the field plate 20. Thus, the FET shown in FIG. 4B is manufactured.

The FET according to Example 3 has normally-off characteristics, and can achieve a high breakdown voltage due to the electric field relaxation effect of the field plate. Therefore, it is suitable for a switching device for power control. In addition, when a negative voltage is applied to the drain electrodes 3 and 4, the channel immediately below the first drain electrode 3 is in a pinch-off state, so that the drain current is cut off and exhibits reverse blocking characteristics. On the other hand, when a positive voltage is applied to the drain electrodes 3 and 4, a drain current flows through the low-resistance second drain electrode 4, so that a low-resistance on-characteristic can be realized.

(Embodiment 4)
Next, a fourth embodiment of the present invention will be described with reference to FIG. 5A.
FIG. 5A is a cross-sectional view of the FET according to the present exemplary embodiment. In the present embodiment, the drain electrode 6 is formed on the channel layer (first semiconductor layer) 11. The side of the drain electrode 6 closer to the gate electrode 2 (first drain region) is in Schottky contact with the channel layer 11. Further, the side of the drain electrode 6 far from the gate electrode 2 (second drain region) is formed in contact with a contact region (third semiconductor layer) 18 made of a high-concentration n-type impurity diffusion layer. By making the impurity concentration of the contact region 18 sufficiently high, the electron tunnel distance is shortened, and the contact characteristic substantially close to ohmic property is realized. Since the other configuration is the same as that of the first embodiment, the description thereof is omitted.

In the FET according to the present embodiment, when a negative voltage is applied to the drain electrode 6, the channel is pinched off under the drain electrode 6 that is not in contact with the contact region 18, and the current blocking is performed by blocking the current flow. Realized. On the other hand, when a positive voltage is applied to the drain voltage 6, a drain current flows through a low-resistance current path formed on the contact region 18, and a low on-resistance is obtained.

(Example 4)
Next, Example 4 which is a specific example of the fourth embodiment will be described. FIG. 5B is a cross-sectional view of the FET according to this example.

This FET is formed on a substrate 12 made of silicon or the like. On the substrate 12, a buffer layer 13 for relaxing lattice mismatch, a channel layer 14 made of In _x Ga _1-x N (0 ≦ x ≦ 1), and Al _y Ga _1-y N (0 <y ≦). An electron supply layer 15 comprising 1) is formed in order. In this embodiment, the buffer layer 13, the channel layer 14, and the electron supply layer 15 correspond to the first semiconductor layer. The range of 0 ≦ x ≦ 0.2 as the composition of the channel layer 14 and the range of 0.1 ≦ y ≦ 0.3 as the composition of the electron supply layer 15 is most suitable for a switching device for power control.

The source electrode 1 is formed on the electron supply layer 15 by ohmic contact. A contact region 18, which is a high-concentration n-type impurity diffusion layer, is formed on the electron supply layer 15 separated from the source electrode 1. Further, the drain electrode 6 is formed so as to be in Schottky contact with the electron supply layer 15 on the source electrode 1 side and in contact with the contact region 18 on the side opposite to the source electrode 1.

The surface of the electron supply layer 15 is covered with a surface protective film 21. In addition, in the opening formed between the source electrode 1 and the drain electrode 6, the electron supply layer 15 and the gate electrode 2 constituting the MIS structure are formed via the gate insulating film 22. A part of the gate electrode 2 rides on the surface protection film 21 and plays a role of reducing electric field concentration as a bowl-shaped field plate 20.

Next, a method for manufacturing the FET according to Example 4 will be described. Here, as an example, the composition of the channel layer 14 is GaN with x = 0 and the composition of the electron supply layer 15 is Al _0.2 Ga _0.8 N with y = 0.2. First, a buffer layer 13 (film thickness 20 nm) made of undoped AlN, a channel layer 14 (film thickness 2 μm) made of undoped GaN, and an undoped Al _0.2 Ga film on a substrate 12 made of silicon, for example, by molecular beam epitaxy. _An electron supply layer 15 (thickness 25 nm) made of _0.8 N is formed in order.

Next, an element isolation mesa (not shown) is formed by etching away a part of the formed laminated structure until the channel layer 14 is exposed. Subsequently, a contact region 18 that is a high-concentration n-type impurity diffusion layer extending from the electron supply layer 15 to the upper portion of the channel layer 14 is formed by ion implantation or the like.

Next, the source electrode 1 is formed on the electron supply layer 15 by evaporating a metal such as Ti / Al. And it is set as ohmic contact by annealing at 650 degreeC. Further, a metal such as Ni / Au is deposited on the electron supply layer 15 to form the Schottky contact drain electrode 6.

Subsequently, a surface protective film 21 made of SiN having a thickness of 50 nm is formed by a plasma CVD method or the like. The electron supply layer 15 is exposed by removing a part of the surface protective film 21 by etching. Further, the recess is formed by etching so that the threshold value becomes positive. A gate insulating film 22 made of SiO ₂ having a thickness of 150 nm is formed by, for example, atmospheric pressure CVD so as to cover the exposed electron supply layer 15. A metal film such as Ni / Au is vapor-deposited thereon to form the MIS structure gate electrode 2 having the field plate 20. Thus, the FET shown in FIG. 5B is manufactured.

The FET according to Example 4 has normally-off characteristics and can achieve a high breakdown voltage due to the electric field relaxation effect of the field plate. Therefore, it is suitable for a switching device for power control. When a negative voltage is applied to the drain electrode 6, the channel immediately below the drain electrode 6 that is not in contact with the contact region is in a pinch-off state, so that the drain current is cut off and exhibits reverse blocking characteristics. On the other hand, when a positive voltage is applied to the drain electrode 6, a drain current flows in a region of the drain electrode 6 that is in contact with the contact region 18, so that a low resistance ON characteristic can be realized.

(Embodiment 5)
Next, a fifth embodiment of the present invention will be described with reference to FIG. 6A.
FIG. 6A is a cross-sectional view of the FET according to the present exemplary embodiment. In the present embodiment, the drain electrode 6 is formed on the channel layer (first semiconductor layer) 11 as in the fourth embodiment. The side of the drain electrode 6 closer to the gate electrode 2 (first drain region) is in Schottky contact with the channel layer 11. Further, the side of the drain electrode 6 far from the source electrode 1 (second drain region) is formed in contact with a contact region (second semiconductor layer) 18 made of a high-concentration n-type impurity diffusion layer. Further, in the present embodiment, unlike the fourth embodiment, a part of the drain electrode 6 on the side close to the source electrode 1 is embedded in the recess formed in the channel layer 11. That is, as shown in FIG. 6A, the drain electrode buried portion 7 is formed. Since the other configuration is the same as that of the first embodiment, the description thereof is omitted.

In the FET according to this embodiment, when a negative voltage is applied to the drain electrode 6, the channel is pinched off under the drain electrode embedded portion 7, and the current blocking is realized by blocking the current flow. . On the other hand, when a positive voltage is applied to the drain electrode 6, a drain current flows through a low-resistance current path formed on the contact region 18, and a low on-resistance is obtained. Further, by providing the drain electrode buried portion 7 in which a part of the drain electrode 6 is formed on the recess, the pinch-off property at the time of the reverse blocking operation can be improved and the leakage current can be suppressed.

(Example 5)
Next, Example 5 which is a specific example of the fifth embodiment will be described. FIG. 6B is a cross-sectional view of the FET according to this example.

This FET is formed on a substrate 12 made of silicon or the like. On the substrate 12, a buffer layer 13 for relaxing lattice mismatch, a channel layer 14 made of In _x Ga _1-x N (0 ≦ x ≦ 1), and Al _y Ga _1-y N (0 <y ≦). An electron supply layer 15 comprising 1) is formed in order. In this embodiment, the buffer layer 13, the channel layer 14, and the electron supply layer 15 correspond to the first semiconductor layer. The range of 0 ≦ x ≦ 0.2 as the composition of the channel layer 14 and the range of 0.1 ≦ y ≦ 0.3 as the composition of the electron supply layer 15 are most suitable for the switching device for power control.

The source electrode 1 is formed on the electron supply layer 15 by ohmic contact. A contact region 18 which is a high-concentration n-type impurity diffusion layer is formed at a position separated from the source electrode 1. Further, the drain electrode 6 is formed so as to be in Schottky contact with the electron supply layer 15 on the source electrode 1 side and in contact with the contact region 18 on the side opposite to the source electrode 1. Further, a part of the drain electrode 6 on the source electrode 1 side is embedded in a recess formed in the electron supply layer 15. As a result, the drain electrode buried portion 7 is formed.

The surface of the electron supply layer 15 is covered with a surface protective film 21. A gate electrode 2 in which an electron supply layer 15 and a MIS structure are formed is formed in an opening formed between the source electrode 1 and the drain electrode 6 via a gate insulating film 22. A part of the gate electrode 2 rides on the surface protection film 21 and plays a role of reducing electric field concentration as a bowl-shaped field plate 20.

Next, a method for manufacturing the FET according to Example 5 will be described. Here, as an example, the composition of the channel layer 14 is GaN with x = 0 and the composition of the electron supply layer 15 is Al _0.2 Ga _0.8 N with y = 0.2. First, a buffer layer 13 (film thickness 20 nm) made of undoped AlN, a channel layer 14 (film thickness 2 μm) made of undoped GaN, and an undoped Al _0.2 Ga film on a substrate 12 made of silicon, for example, by molecular beam epitaxy. _An electron supply layer 15 (thickness 25 nm) made of _0.8 N is formed in order.

Next, an element isolation mesa (not shown) is formed by etching away a part of the formed laminated structure until the channel layer 14 is exposed. Subsequently, a contact region 18 that is a high-concentration n-type impurity diffusion layer extending from the electron supply layer 15 to the upper portion of the channel layer 14 is formed by ion implantation or the like.

Next, the source electrode 1 is formed on the electron supply layer 15 by evaporating a metal such as Ti / Al. And it is set as ohmic contact by annealing at 650 degreeC. Further, a recess in which a part of the electron supply layer 15 is removed by etching is formed in the vicinity of the contact region 18. Then, a metal such as Ni / Au is deposited on the electron supply layer 15 to form the Schottky contact drain electrode 6. The drain electrode 6 is formed so as to cover both the contact region 18 and the recess. The portion buried in the recess becomes the drain electrode buried portion 7.

Subsequently, a surface protective film 21 made of SiN having a thickness of 50 nm is formed by a plasma CVD method or the like. The electron supply layer 15 is exposed by removing a part of the surface protective film 21 by etching. Further, the recess is formed by etching so that the threshold value becomes positive. A gate insulating film 22 made of SiO ₂ having a thickness of 150 nm is formed by, for example, atmospheric pressure CVD so as to cover the exposed electron supply layer 15. A metal film such as Ni / Au is vapor-deposited thereon to form the MIS structure gate electrode 2 having the field plate 20. Thus, the FET shown in FIG. 6B is manufactured.

The FET according to Example 5 has normally-off characteristics and can achieve a high breakdown voltage due to the electric field relaxation effect of the field plate. Therefore, it is suitable for a switching device for power control. When a negative voltage is applied to the drain electrode 6, the channel layer 14 immediately below the drain electrode 6 that is not in contact with the contact region 18 is in a pinch-off state, so that the drain current is cut off and exhibits reverse blocking characteristics. On the other hand, when a positive voltage is applied to the drain electrode 6, a drain current flows in a region of the drain electrode 6 that is in contact with the contact region 18, so that a low resistance ON characteristic can be realized. Further, the FET of this embodiment is one in which a part of the drain electrode 6 is formed on the recess in the fourth embodiment. Therefore, the pinch-off property during the reverse blocking operation can be improved and the leakage current can be suppressed.

(Embodiment 6)
Next, a sixth embodiment of the present invention will be described with reference to FIG. 7A.
FIG. 7A is a cross-sectional view of the FET according to the present exemplary embodiment. In the present embodiment, a contact layer (third semiconductor layer) 19 that is a high-concentration n-type epitaxial layer is formed on the channel layer (first semiconductor layer) 11. On the contact layer 19, an ohmic contact source electrode 1 and a Schottky contact drain electrode 6 are formed. By making the impurity concentration of the contact layer 19 that is in contact with the side of the drain electrode 6 far from the gate electrode 2 (second drain region) sufficiently high, the electron tunneling distance is shortened and contact characteristics substantially close to ohmic characteristics are obtained. Realize. In addition, a recess that penetrates the contact layer 19 and reaches the n-type channel layer is formed in a part of the n-type contact layer 19 on which the drain electrode 6 is formed on the side close to the source electrode 1. A part of the drain electrode 6 is buried inside the recess, and a drain electrode buried portion (first drain region) 7 is formed. Since the other configuration is the same as that of the first embodiment, the description thereof is omitted.

In the FET according to this embodiment, when a negative voltage is applied to the drain electrode 6, the channel is pinched off under the drain electrode embedded portion 7, and the current blocking is realized by blocking the current flow. . On the other hand, when a positive voltage is applied to the drain electrode 6, the drain current flows through a low-resistance current path formed on the contact layer 19, and a low on-resistance is obtained. The FET of this example is a contact layer 19 that is an epitaxial layer instead of the contact region 18 in the fifth embodiment. Thereby, performance equivalent to that of the fifth embodiment can be realized with good controllability.

(Example 6)
Next, Example 6 which is a specific example of the sixth embodiment will be described. FIG. 7B is a cross-sectional view of the FET according to this example.

This FET is formed on a substrate 12 made of silicon or the like. On the substrate 12, a buffer layer 13 for relaxing lattice mismatch, a channel layer 14 made of In _x Ga _1-x N (0 ≦ x ≦ 1), and Al _y Ga _1-y N (0 <y ≦). An electron supply layer 15 comprising 1) is formed in order. In this embodiment, the buffer layer 13, the channel layer 14, and the electron supply layer 15 correspond to the first semiconductor layer. The range of 0 ≦ x ≦ 0.2 as the composition of the channel layer 14 and the range of 0.1 ≦ y ≦ 0.3 as the composition of the electron supply layer 15 are most suitable for the switching device for power control. On the electron supply layer 15, a contact layer 19 made of n-type AlGaN doped with n-type and having the same composition is formed.

The source electrode 1 in ohmic contact is formed on the contact layer 19. A drain electrode 6 is formed on the contact layer 19 separated from the source electrode 1 by Schottky contact. A part of the drain electrode 6 on the side close to the source electrode 1 is embedded in a recess that penetrates the contact layer 19 and reaches the electron supply layer 15. This portion forms the drain electrode buried portion 7.

In the region between the source electrode 1 and the drain electrode 6, the contact layer 19 is removed. The exposed surface of the electron supply layer 15 is covered with the surface protective film 21. Then, the gate electrode 2 in which the electron supply layer 15 and the MIS structure are formed is formed in the opening between the source electrode 1 and the drain electrode 6 through the gate insulating film 22. A part of the gate electrode 2 rides on the surface protective film 21 and plays a role of reducing electric field concentration as a bowl-shaped field plate 20.

Next, a method for manufacturing the FET according to Example 6 will be described. Here, as an example, the composition of the channel layer 14 is GaN with x = 0 and the composition of the electron supply layer 15 is Al _0.2 Ga _0.8 N with y = 0.2. First, a buffer layer 13 (film thickness 20 nm) made of undoped AlN, a channel layer 14 (film thickness 2 μm) made of undoped GaN, and an undoped Al _0.2 Ga film on a substrate 12 made of silicon, for example, by molecular beam epitaxy. _An electron supply layer 15 (film thickness 25 nm) made of _0.8 N and a contact layer 19 (film thickness 25 nm, impurity concentration 1 × 10 ¹⁹ cm ⁻³ ) made of n-type AlGaN are sequentially formed.

Next, an element isolation mesa (not shown) is formed by etching away a part of the formed laminated structure until the channel layer 14 is exposed. Subsequently, the source electrode 1 is formed on the contact layer 19 by evaporating a metal such as Ti / Al. And it is set as ohmic contact by annealing at 650 degreeC. Further, a recess that penetrates the contact layer 19 and reaches the electron supply layer 15 is formed by etching at a position where the drain electrode buried portion 7 is formed. Then, a metal such as Ni / Au is deposited so as to be in contact with the electron supply layer 15 to form the Schottky contact drain electrode 6. Of these, the portion buried in the recess becomes the drain electrode buried portion 7.

Subsequently, the contact layer 19 between the source electrode 1 and the drain electrode 6 is removed by etching, and the electron supply layer 15 is exposed. Subsequently, a surface protective film 21 made of SiN having a thickness of 50 nm is formed by a plasma CVD method or the like. The electron supply layer 15 is exposed by removing a part of the surface protective film 21 by etching. Then, a recess is formed by etching so that the threshold value becomes positive. A gate insulating film 22 made of SiO ₂ having a thickness of 150 nm is formed by, for example, atmospheric pressure CVD so as to cover the exposed electron supply layer 15. On top of that, a metal such as Ni / Au is vapor-deposited to form the gate electrode 2 having the MIS structure having the field plate 20. Thus, the FET shown in FIG. 7B is manufactured.

The FET according to Example 6 has normally-off characteristics and can achieve a high breakdown voltage due to the electric field relaxation effect of the field plate. Therefore, it is suitable for a switching device for power control. When a negative voltage is applied to the drain electrode 6, the channel layer 14 immediately below the drain electrode 6 that is not in contact with the contact layer 19 is in a pinch-off state, so that the drain current is cut off and exhibits reverse blocking characteristics. On the other hand, when a positive voltage is applied to the drain electrode 6, a drain current flows in a region of the drain electrode 6 that is in contact with the contact region 18, so that a low resistance ON characteristic can be realized. In the FET of this embodiment, a contact layer 19 that is an epitaxial layer is formed in place of the contact region 18 in the fifth embodiment. Therefore, performance equivalent to that of the fifth embodiment can be realized with good controllability.

(Embodiment 7)
Next, a seventh embodiment of the present invention will be described with reference to FIG. 8A.
FIG. 8A is a cross-sectional view of the FET according to the present exemplary embodiment. In the present embodiment, a contact layer (third semiconductor layer) 19 that is a high-concentration n-type epitaxial layer is formed on the channel layer (first semiconductor layer) 11. On the contact layer 19, an ohmic contact source electrode 1 and a Schottky contact drain electrode 6 are formed. By making the impurity concentration of the contact layer 19 that is in contact with the side of the drain electrode 6 far from the gate electrode 2 (second drain region) sufficiently high, the electron tunneling distance is shortened and contact characteristics substantially close to ohmic characteristics are obtained. Realize. In addition, a recess that penetrates the contact layer 19 and reaches the channel layer 11 is formed in a part of the n-type contact layer 19 on which the drain electrode 6 is formed on the side close to the source electrode 1. Inside the recess, a part of the drain electrode 6 is buried via the insulating film 5, and a drain electrode buried portion (first drain region) 7 is formed. That is, the drain electrode buried portion 7 forms a MIS structure with the channel layer 11. Since the other configuration is the same as that of the first embodiment, the description thereof is omitted.

In the FET according to this embodiment, when a negative voltage is applied to the drain electrode 6, the channel is pinched off under the drain electrode embedded portion 7, and the current blocking is realized by blocking the current flow. . On the other hand, when a positive voltage is applied to the drain electrode 6, the drain current flows through a low-resistance current path formed on the contact layer 19, and a low on-resistance is obtained. In the FET of this example, the drain electrode buried portion 7 in the sixth embodiment has a MIS structure, and the leakage current during the reverse blocking operation can be reduced as compared with the sixth embodiment.

(Example 7)
Next, Example 7 which is a specific example of the seventh embodiment will be described. FIG. 8B is a cross-sectional view of the FET according to this example.

This FET is formed on a substrate 12 made of silicon or the like. On the substrate 12, a buffer layer 13 for relaxing lattice mismatch, a channel layer 14 made of In _x Ga _1-x N (0 ≦ x ≦ 1), and Al _y Ga _1-y N (0 <y ≦). An electron supply layer 15 comprising 1) is formed in order. In this embodiment, the buffer layer 13, the channel layer 14, and the electron supply layer 15 correspond to the first semiconductor layer. The range of 0 ≦ x ≦ 0.2 as the composition of the channel layer 14 and the range of 0.1 ≦ y ≦ 0.3 as the composition of the electron supply layer 15 are most suitable for the switching device for power control. On the electron supply layer 15, a contact layer 19 made of n-type AlGaN having the same composition and doped n-type is disposed.

The source electrode 1 in ohmic contact is formed on the contact layer 19. On the contact layer 19 spaced apart from the source electrode 1, the Schottky contact drain electrode 6 is formed. A part of the drain electrode 6 on the side close to the source electrode 1 is embedded in a recess that penetrates the contact layer 19 and reaches the electron supply layer 15. This portion forms the drain electrode buried portion 7. A gate insulating film 22 is formed between the drain electrode buried portion 7 and the electron supply layer 15 in the recess. That is, the drain electrode buried portion 7 forms an MIS structure with the electron supply layer 15.

In the region between the source electrode 1 and the drain electrode 6, the contact layer 19 is removed. The exposed surface of the electron supply layer 15 is covered with the surface protective film 21. Then, the gate electrode 2 in which the electron supply layer 15 and the MIS structure are formed is formed in the opening between the source electrode 1 and the drain electrode 6 through the gate insulating film 22. A part of the gate electrode 2 rides on the surface protective film 21 and plays a role of reducing electric field concentration as a bowl-shaped field plate 20.

Next, a method for manufacturing the FET according to Example 7 will be described. Here, as an example, the composition of the channel layer 14 is GaN with x = 0 and the composition of the electron supply layer 15 is Al _0.2 Ga _0.8 N with y = 0.2. First, a buffer layer 13 (film thickness 20 nm) made of undoped AlN, a channel layer 14 (film thickness 2 μm) made of undoped GaN, and an undoped Al _0.2 Ga film on a substrate 12 made of silicon, for example, by molecular beam epitaxy. _An electron supply layer 15 (film thickness 25 nm) made of _0.8 N and a contact layer 19 (film thickness 25 nm, impurity concentration 1 × 10 ¹⁹ cm ⁻³ ) made of n-type AlGaN are sequentially formed.

Next, an element isolation mesa (not shown) is formed by etching away a part of the formed laminated structure until the channel layer 14 is exposed. Subsequently, the source electrode 1 is formed on the contact layer 19 by evaporating a metal such as Ti / Al. And it is set as ohmic contact by annealing at 650 degreeC. Subsequently, a recess that penetrates the contact layer 19 and reaches the electron supply layer 15 is formed by etching at a position where the drain electrode buried portion 7 is formed.

Further, the contact layer 19 around the gate electrode formation region is removed by etching to expose the electron supply layer 15. Subsequently, a surface protective film 21 made of SiN having a thickness of 50 nm is formed by a plasma CVD method or the like. The AlGaN electron supply layer 15 is exposed by etching away a part of the surface protective film 21. Then, a recess is formed by etching so that the threshold value becomes positive. Here, the surface protective film 21 on the contact layer 19 forming the drain electrode 6 is also removed. A gate insulating film 22 made of SiO ₂ having a thickness of 150 nm is formed by, for example, atmospheric pressure CVD so as to cover the exposed electron supply layer 15 and contact layer 19. After removing the gate insulating film 22 on the upper surface of the contact layer 19, a metal such as Ni / Au is vapor-deposited to form the gate electrode 2 and the drain electrode 6 having the MIS structure having the field plate 20. Thus, the FET shown in FIG. 8B is manufactured.

The FET according to Example 7 has normally-off characteristics and can achieve a high breakdown voltage due to the electric field relaxation effect of the field plate. Therefore, it is suitable for a switching device for power control. When a negative voltage is applied to the drain electrode 6, the drain electrode 6 that is not in contact with the contact region, that is, the channel immediately below the drain electrode buried portion 7 is in a pinch-off state, so that the drain current is cut off and reverse blocking characteristics are exhibited. On the other hand, when a positive voltage is applied to the drain electrode 6, a drain current flows in a region of the drain electrode 6 that is in contact with the contact region 18, so that a low resistance ON characteristic can be realized. The FET of this embodiment has the drain electrode buried portion 7 having the MIS structure in the sixth embodiment, and can reduce the leakage current during the reverse blocking operation as compared with the sixth embodiment.

The present invention has been described above with reference to the embodiment, but the present invention is not limited to the above. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

This application claims priority based on Japanese Patent Application No. 2009-007395 filed on Jan. 16, 2009, the entire disclosure of which is incorporated herein.

The present invention is applicable to, for example, a direct conversion type power conversion circuit.

DESCRIPTION OF SYMBOLS 1 Source electrode 2 Gate electrode 3 1st drain electrode 4 2nd drain electrode 5 Insulating film 6 Drain electrode 7 Drain electrode embedding part 10 Substrate 11 Channel layer 12 Substrate 13 Buffer layer 14 Channel layer 15 Electron supply layer 16 P-type layer 18 Contact region 19 Contact layer 20 Field plate 21 Surface protective film 22 Gate insulating film

Claims (15)

A first semiconductor layer including a channel layer;
A source electrode formed on the first semiconductor layer;
A drain electrode formed on the first semiconductor layer and spaced apart from the source electrode;
A gate electrode formed between the source electrode and the drain electrode on the first semiconductor layer;
The drain electrode is
A first drain region in which a reverse current between the first semiconductor layer and the first semiconductor layer is blocked;
And a second drain region that is formed farther from the gate electrode than the first drain region and has a lower resistance to the first semiconductor layer than the first drain region. The semiconductor device according to claim 1, wherein the first drain region is in Schottky contact with the first semiconductor layer. 2. The semiconductor device according to claim 1, wherein an insulating film is formed between the first drain region and the first semiconductor layer to form a MIS structure. 2. The semiconductor device according to claim 1, wherein a second semiconductor layer having a conductivity type different from that of the first semiconductor layer is formed between the first drain region and the first semiconductor layer. The semiconductor device according to any one of claims 1 to 4, wherein the first drain region and the second drain region are integrally formed. The semiconductor device according to any one of claims 1 to 4, wherein the first drain region and the second drain region are formed separately. The semiconductor device according to any one of claims 1 to 6, wherein a recess is formed in the first semiconductor layer, and the first drain region is formed on the recess. A third semiconductor layer having the same conductivity type as the first semiconductor layer and having a higher impurity concentration than the first semiconductor layer is formed between the second drain region and the first semiconductor layer. The semiconductor device according to any one of claims 1 to 7, wherein: 9. The semiconductor device according to claim 8, wherein the third semiconductor layer is a diffusion layer formed inside the first semiconductor layer. The semiconductor device according to claim 8, wherein the third semiconductor layer is an epitaxial layer formed on the first semiconductor layer. The semiconductor device according to any one of claims 1 to 10, wherein the source electrode is in ohmic contact with the first semiconductor layer. The semiconductor device according to any one of claims 1 to 11, wherein the gate electrode is in Schottky contact with the first semiconductor layer. 12. The semiconductor device according to claim 1, wherein an insulating film is formed between the gate electrode and the first semiconductor layer to form a MIS structure. The semiconductor device according to any one of claims 1 to 13, wherein the first semiconductor layer includes a heterojunction of semiconductor layers having different band gaps. Forming a first semiconductor layer including a channel layer;
Forming a source electrode, a drain electrode, and a gate electrode between the source electrode and the drain electrode on the first semiconductor layer, and
The drain electrode is
A first drain region in which a reverse current between the first semiconductor layer and the first semiconductor layer is blocked;
And a second drain region formed farther from the gate electrode than the first drain region and having a lower resistance to the first semiconductor layer than the first drain region. .

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